South Korea's foreign reserves declined for the first time in three months amid the recent appreciation of the U.S. dollar.

According to the Bank of Korea(BOK) on Monday, the nation's foreign currency reserves stood at 420-point-98 billion dollars as of the end of last month, down by five-point-seven billion dollars from a month earlier.

The reserves had expanded for two consecutive months through April, driven by the boosted value of non-dollar assets due to a weaker dollar.

A BOK official pointed to a climb last month of two-point-six percent in the U.S. dollar index, which measures the greenback’s strength against a basket of six other widely traded currencies, dragging the value of non-dollar assets back down.

Measures aimed at stabilizing the foreign exchange market was also responsible, the official added.

As of the end of April, South Korea was the world's ninth-largest holder of foreign exchange reserves. China topped the list at over three trillion dollars, followed by Japan, Switzerland and Russia.